The striatum is critically involved in the planning and execution of directed movement, and numerous neurological disorders are closely associated with striatal dysfunction. Despite a detailed understanding of striatal cellular and circuit function, and compelling evidence that striatal function is to a large extent governed by highly structured corticostriatal input, the intracortical mechanisms responsible for shaping and providing this input remain unknown. I propose to elucidate these mechanisms by characterizing the intrinsic membrane properties and morphologies of the two major corticostriatal layer V pyramidal populations, determine whether they, like some other pyramidal cell classes, form subnetworks of preferential homotypic connections, and whether they are subject to differential local inhibition. Results from these experiments will not only clarify the cortical determinants of corticostriatal activity but, by asking whether functionally related layer V pyramidal cells form distinct or overlapping local networks, will also provide insight into the principles of cortical circuit organization. [unreadable] [unreadable] [unreadable]